In the fabrication of microelectronic components, a number of the steps involved, for instance, in preparing integrated circuit chips and the packaging for the chips (articles to which the chips are attached for electrical interfacing and/or protection), are cleaning and etching processes. Accordingly, over the years, a number of vastly different types of etching processes to remove material, sometimes in selective areas, have been developed and are utilized to varying degrees. Moreover, the steps of etching different layers which constitute, for instance, the finished integrated circuit chip are among the most critical and crucial steps.
For example, producing an oxide-free silicon surface for rendering it ready for subsequent processing is often essential. In many processes, the silicon wafer, used in the production of integrated circuit chips, is processed to form wells along with desired isolation. Typically, an oxide layer may be thermally grown on the silicon substrate for protecting previously formed active silicon regions against adverse effects from subsequent processing steps, as well as for removing (by oxidation) the near or top surface silicon which may have been damaged or contaminated in the previous processing.
However, at some further point in the manufacturing process, this sacrificial silicon oxide layer typically must be removed to provide an oxide-free silicon surface (e.g. for construction of further features of the desired integrated circuit design). Where a gate is to be formed, this oxide removal step is commonly referred to as pre-gate cleaning. This cleaning is performed in an aqueous medium followed by a deionized water rinse or as a vapor-phase process using HF vapor. One of the problems related to aqueous processing is the appearance of water stains after the drying (water drying marks). These stains are becoming more and more of an issue in device manufacture as device dimensions are shrinking.
The mechanism behind the water stain formation is that water itself is a very aggressive chemical towards the bare silicon surface (more aggressive than HF for instance) and is a very good solvent for silica (silicon dioxide). During the rinsing process, silicon and silica dissolve in very small quantities in the deionized water forming mono-molecular soluble or colloidally-dispersed silicic acid (non-ionic because of the neutral pH of deionized water). Due to its has an extremely low solubility, its non-ionic nature and its non-volatility, the silicic acid deposits on the silicon wafer surface when the deionized water evaporates in the dryer. Other drying residues can originate from any intrinsic contaminants the still present in the already highly purified deionized water.
In addition to staining problems, the processes of the prior art often result in undesired roughening of the silicon surface.
It would therefore be desirable to provide a procedure capable of removing silicon oxide layers to render a surface oxide-free while avoiding or minimizing the problems associated with conventional deionized water-based processes.